Method of treating and cold deep drawing sheet metal



Patented Aug. 17 1954 OFFICE METHOD OF TREATING AND COLD DEEP DRAWING SHEET METAL Harley A. Montgomery, Detroit, Mich.

No Drawing. Application January 14, 1948, Serial No. 2,331

3 Claims. 1' i This invention relates to a method of treating metal to be shaped by cold deformation by means of dies or the like to protect the surface thereof from marring or scratching and more particularly to a method of treatment in which a tough plastic film is applied to the surface of the metal.

In the mechanical art of forming or shaping metal parts by cold deformation of rolled metal sheets or strips with high surface finish, it is extremely desirable that the slightest marking o marring of the metal surfaces be avoided so as to eliminate subsequent polishing operations which would be needed to remove these blemishes.

To accomplish this objective it is necessary that the surface of the die and the work piece be prevented from coming together closely enough to result in metal-to-metal contact; that is at present effected by the maintenance between these surfaces of a tough plastic interracial film, indestructible under conditions of normal operation.

The most efficient film for this purpose has been found to be a varnish or lacquer-like film, applied to the surface in a solvent which was then allowed to evaporate and leave a dry film. While this does an excellent job of preventing metal-to-metal contact, it has a number of ob- ,iectionable features. First of all, the solvents involved are often toxic or present a grave fire hazard. But what is more important, after the forming operation is complete, the film has to be removed and this cannot readily be done except by the expensive and hazardous solvents similar to those in which the film was originally dissolved.

To meet these objections there have been and are being used, alkali soap film deposited from hot aqueous solutions. The parts are dipped in these hot soap solutions, are allowed to dry, sometimes with the aid of special heating equipment, and the metal is then formed. The remaining film is then subsequently readily removed by hot water or mild alkali washes normally available in industry for this purpose.

In order to obtain a sufiiciently thick soap film to give adequate protection to the metal surfaces, in the solutions of this type it has been found necessary to body up the soap solution by the addition of large percentages of mild alkali salt, sodium tetraborate, trisodium phosphate, etc. A typical solution of this kind would contain 5 ounces of soda soap and 11 ounces of borax dissolved in a gallon of water. This, even at temperatures approaching the boiling point gives solutions of rather high viscosity and as a result the metal parts immersed in and withdrawn from the hot solutions receive a substantial coating when subsequently dried. The alkali salts present act to some extent as water soluble pigments to fortify the soap film in the subsequent metal forming operations.

While the films of this type have functioned moderately successfully in the type of operation under discussion, they are not as efficient as the lacquer type films in preventing marring or scratching. This is probably due to the fact that these films on cooling are of a slimy gelatinous nature and, owing to their thickness, are not very readily completely dried. In the presence of any appreciable amount of water, the film is similar to that with which We are all familiar in the case of household soap which has been allowed to lie in water; it is of a soft gelatinous nature with no film strength whatever; when, however, all or most of the water is removed the film strength becomes very high.

The present invention has for its object to provide a tough lacquer-like protective film that is very effective to prevent marring or scratching of the metal surface and that can be readily removed by washing with hot water or with a mild alkali solution.

I have found that aqueous solutions of sodium or potassium resinates will dry rapidly and form a non-gelatinous lacquer-like transparent film which effectively protects the metal from marring or scratching during the shaping operation. The resinates employed are salts of acids known as resin acids and are preferably the resinates that are produced commercially by processes in which rosin is treated with a caustic alkali to form the alkali salts of the mixture of acids of which the rosin is composed.

Due to the great solubility of the resinates in water, high concentrations of resinates may be employed which when applied to the metal will form films which will dry rapidly and form a tough, non-gelatinous, lacquer-like, transparent film which is much more effective to prevent marring or scratching than aqueous solutions or emulsions heretofore used and which is also readily removed by hot water or mild alkali washes when that is desired.

Sodium and potassium resinates are commercially available at moderate cost. Sodium resinates are usually in the form of a dry powder such as Dresinate X sold by Hercules Powder Company, and the potassium resinates in the form of a viscous liquid containing solids and 10% water such as Dresinate 90 sold by 3 Hercules Powder Company. I prefer to use the sodium resinate in those cases where an extremely tough film is needed and a fihn of high frictional resistance can be tolerated, as in the shaping of heavy metal parts. Where, however, the metal is of light gauge (.020" thickness or less) and a film of lower frictional resistance is desirable, I use a solution of the potassium resinate.

The method of the present invention aiIords protection to metal surfaces during shaping operations equal to that provided by the application of lacquer films and eliminates the hazards and much of the expense incident to the application and removal of lacquer films.

What I claim is:

1. The method of cold deformation of sheet metals which comprises applying to a metal workpiece a thin coating of an aqueous solution of a resinate of the group consisting of sodium resinate and potassium resinate, drying the coating, deep drawing the coated workpiece without marring the surface thereof, and removing the coating by washing with a mildly alkaline aqueous solution.

2. A method as defined in claim 1 in which the resinate is sodium resinate.

3. A method as defined in claim 1 in which the resinate is potassium resinate.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 82,675 Barrett Oct. 6, 1868 1,683,437 Batie Sept. 4, 1928 1,769,577 Hopkins July 1, 1930 2,120,461 Copeman June 14, 1938 2,126,123 Montgomery Aug. 9, 1938 2,140,131 Helfrick Dec. 13, 1938 2,145,252 Engle Jan. 31, 1939 2,199,627 French May 7, 1940 2,305,560 Schiermeier Dec. 15, 1942 2,323,471 Humphrey July 6, 1943 2,329,731 Spring Sept. 21, 1943 2,343,036 Wilson Feb. 29, 1944 2,383,906 Zimmer Aug. 28, 1945 2,413,121 Sevenson Dec. 24, 1946 2,463,823 Weitkamp Mar. 8, 1949 

1. THE METHOD OF COLD DEFORMATION OF SHEET METALS WHICH COMPRISES APPLYING TO A METAL WORKPIECE A THIN COATING OF AN AQUEOUS SOLUTION OF A RESINATE OF THE GROUP CONSISTING OF SODIUM RESINATE AND POTASSIUM RESINATE, DRYING THE COATING, DEEP DRAWING THE COATED WORKPIECE WITHOUT MARRING THE SURFACE THEREOF, AND REMOVING THE COATING BY WASHING WITH A MILDLY ALKALINE AQUEOUS SOLUTION. 